Inductive power transfer (IPT) systems provide one example of wireless transfer of energy. In IPT, a primary (or “transmitter”) power device transmits power to a secondary (or “receiver”) power device. Each of the transmitter and receiver power devices include an inductive coupler, typically a single coil or a multi coil arrangement of windings comprising electric current conveying materials. An alternating current passing through the primary inductor produces an alternating magnetic field. When the secondary inductor is placed in proximity to the primary inductor, the alternating magnetic field induces an electromotive force (EMF) in the secondary inductor according to Faraday's law, thereby transferring power to the secondary power receiver device. Typically, frequencies in the very low frequency (VLF) or low frequency (LF) bands e.g. in the range from 20 kHz to 150 kHz, are used for IPT in vehicle charging applications.
Inductive power transfer to vehicles at power levels of several kilowatts in both domestic and public parking zones may require special protective measures for safety of persons and equipment in proximity. Such measures may include detection of foreign objects in the critical space of an IPT system, especially where such foreign objects are subject to excessive eddy currents and heating if exposed to strong alternating magnetic fields. This may be particularly true for systems where the critical space is open and accessible. Such measures may also include detection of living objects, for example humans, extremities of humans, or animals, to protect them from exposure to such strong electromagnetic fields.
The critical space of an IPT system may be defined as the space where electromagnetic field levels exceed certain critical levels. These levels may be based on regulatory limits for human exposure, magnetic flux density limits determined by eddy current heating effects in foreign metallic objects, or other limits such as those specified by a standard applicable to a particular product or to a particular use case. As such, systems, methods, and apparatuses for radar-based detection of objects in a predetermined space are desirable.